Hereditary Spastic Paraplegia (HSP) is a neurological disorder characterized by spasticity and weakness of the lower extremities. HSP is progressive, has no known treatment and affected subjects frequently become wheelchairdependent. Neuropathologic studies showed degeneration at the distal ends of the longest axons in the central nervous system. Recently, two HSP genes have been cloned, paraplegin causing AR HSP linked to chromosome 16 and spastin causing the most common type of AD HSP linked to chromosome 2p. In spite this progress, the pathophysiology of HSP remains elusive. I analyzed large kindred with AD HSP that was not linked to previously known loci. A genomewide search identified a tight linkage to chromosome 8q2324 and thus, I established a novel locus for AD HSP, designated as SPG8. Our collaborator, Dr. Reid, has identified one additional family linked to the same locus and reduced the locus. A BAC based 388 kb and several genes are present in the region. Two BACs have been sequenced and data is available in a public database. The sequencing of the third BAC is underway. I propose to clone the gene causing SPG8. I will analyze all identified genes in the contig and prioritize candidate genes based on their known function and homology to other genes known genes. I will sequence all predicted genes from 3 BACs spanning the SPG8 locus. If no mutations are found in these genes, I will identify other genes by direct cDNA selection and exon trapping. If no mutation is found using this approach I will clone and sequence regulatory segments of identified genes and search for mutations. Cloning of the SPG8 gene will allow me to create a mouse model by manipulation of the murine genome. The approach to generate a transgenic mouse model will depend on identified pathophysiology of SPG8. If mutations in the SPG8 gene cause HSP due to haplo-insufficiency, I will use homologous recombination approach. If dominantnegative mechanism is likely I will create a transgenic mouse expressing SPG8 mutation. I will characterize the phenotype of transgenic animals. The study of a transgenic animal model will further enhance current state of knowledge about the pathophysiology of HSP and axonal degeneration.